Font Size: a A A

Initial Study On Geological And Geochemical Characteristics Of The Yanzigou Gold Deposit, Danba

Posted on:2011-03-29Degree:MasterType:Thesis
Country:ChinaCandidate:L HouFull Text:PDF
GTID:2120360308959106Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
Tectonic position of the study area was located at the east margin of the passive continental of Yangzi Plate. Strata of studying area belongs to Danba deep detachment - superimposed tectonic slices unit, outcrop is Devonian Weiguan Group .Yanzigou gold deposit situated the central of Yongxi fornix, the west of Tonglufang anticline, a special place where the territorial deep-great faults of Donggu and Lianghekou and Maoniuhe is intercorss and tectonic deformation is intricate and intense.These tectonic elements macroscopily controls the establishment of the gold deposit.The ore bodys in Yanzigou gold deposit mainly occur in the black carbonaceous slate and the gray-green quartz sericite phyllite of Devonian Weiguan Group. As the roof or bottom of ore body, the black carbonaceous slate is a geochemical barrier and has played a good obstructing effect for the ore fluid's enrichment, and as a good chemical barrier due to its high C,S.Ore mining area is divided into three blocks-Mozigou ore block, Nichonggou ore block and Yanzigou ore block. According to the composition of the ore minerals, the ore can bedivided into quartz vein gold ore and carbonaceous slate type layered gold ore which has a dense network of quartz veins and pyrite. The metal minerals are mainly sulfide in hydrothermal stage, pyrite framboid in the sedimentary diagenetic period, hydrothermal over-growth zoning pyrite in different ore-forming stage. Ore structure is brecciated, veiny, ribbon, earthy and the texture is automorphic- hypautomorphic granular , over-growth zoning , allotriomorphic granular , replacement remnant and pseudomorphic. Gold mineral is mainly occured in pyrite, chalcopyrite and limonite as inclusion gold, fissure gold. Wall-rock alteration is rich, the main alteration is siliconization, beresitization, epidotization, ferritization,etc.According to the geological setting and geochemical characteristics, metallogenic evolution of the deposit is divided into hydrothermal sedimentation period, hydrothermal stage, supergene stage. Hydrothermal stage is the mainly metallogenic period,combined with the Ore-controlling structure's deformation sequence, mineralization, alteration and mineral assemblage, it can be divided further into quartz-pyrite stage, gold- sulfide -quartz stage, quartz-calcite stage.The major elements , trace elements and rare earth elements in ores indicate that mineralized components have inheritance from wall rock, metallogenic elements have the Au-Ag-Cu-Pb-Zn assemblage characteristics.The formation of the wall rock has both the characteristics of hydromorphic and hydrothermal, demonstrating its formation is complex. The characters of hydrogen and oxygen isotopes,and compositions of fliud inclusions indicate that the ore fluids are maily divided into two stages, the earlier stage is meramorphic water that is transformated by strong tectonizations, the later stage is mixed hydrothermal combined with precipitate water. Elements characteristics and lead isotope possesses the feature of orogenic,this indicates the orogenic settings and mineralizing dynamics come from the intracontinental orogenic action. Sulfur isotope possesses that sulfur is coming from both wall rock and magmatic rock . Fluid inclusions are divided into carbonaceous inclusions and aqueous inclusions, the first one has the typical characteristics of orogenic gold deposit metamorphic hydrotherm, whose homogenization temperature is medium (220~380℃),low salinity(6.97~15.42%NaCl eqv),low density(0.95~1.00 g/cm3), high CO2 contents, fluid pressure is 172 Mpa, metallogenic depth is about 6.7km. The second one has lower homogenization temperature (100~220℃) , low salinity(2.82~15.00%NaCl eqv),low density(0.20~0.38 g/cm3), there is hardly any CO2, fluid pressure is 172 Mpa, metallogenic depth is about 6.7km, these indicates that these inclusions have the characteristics of precipitate water . The metallogenic fluid is acidic (pH around 4.27-5.45) ,with high sulfur fugacity(-6.16~-16.37),low oxygen fugacity(-27.47~-42.35),which belongs to relative reducing env environmen(tEh around -0.02~-0.33). In mineralizing processes, gold metals are mainly migration as sulfide complex,and deposited when the chemical composition condition and temperature, pressure change.According to the geochemistry character of Yanzigou gold deposit, suggests that it belongs to orogenic gold deposit.
Keywords/Search Tags:Songpan-Ganzi orogenic belt, Yanzigou, ore geochemistry, orogenic gold deposit
PDF Full Text Request
Related items